Semiconductor integrated circuits in which a semiconductor laser and an optical modulator are integrated together have been known, as disclosed, e.g., in Published Japanese Translation of PCT Application No. 2002-533940. Paragraph [008] of this publication mentions that the difference in wavelength between photonic devices on a substrate may be dependent on their positions on the substrate, and that the difference in wavelength between a laser and a modulator therefor, called detuning, is important. This publication describes a circuit mask for manufacturing a laser and a modulator on a substrate, said circuit mask including two mask portions (i.e., a laser mask portion and a modulator mask portion), and discloses a method for determining the width of the modulator portion (or modulator mask portion) in order to achieve necessary wavelength compensation.
Other prior art includes Japanese Laid-Open Patent Publication No. 2002-033547.
Optical modulators in which a laser diode section (also referred to hereinafter as an LD section) and an electroabsorption modulator section (also referred to hereinafter as an EAM section) are integrated together are manufactured by forming the LD section and the EAM section on the same substrate. The principal performance of such integrated optical modulators depends on the absorption spectrum of the EAM section, the lasing wavelength of the LD section, and the difference between these wavelengths. It should be noted that the difference between the lasing wavelength of the LD section and the photoluminescent wavelength of the EAM section is preferably as close to the design value as possible (this difference being also referred to hereinafter as Δλ).
However, the lasing wavelength of the LD section varies to a certain extent due to manufacturing variations of the LD section, and the photoluminescent wavelength of the EAM section also varies to a certain extent due to manufacturing variations of the electroabsorption layer (or EAM absorption layer). These variations in the lasing wavelength of the LD section and in the photoluminescent wavelength of the EAM section may be such that the Δλ of the optical modulator varies beyond tolerance limits.